1. Field of the Invention
In at least one aspect, the present invention is related to stabilization of electrodes for fuel cell applications.
2. Background Art
Fuel cells are used as an electrical power source in many applications. In particular, fuel cells are proposed for use in automobiles to replace internal combustion engines. A commonly used fuel cell design uses a solid polymer electrolyte (“SPE”) membrane or proton exchange membrane (“PEM”), to provide ion transport between the anode and cathode.
In the PEM type fuel cells, hydrogen is supplied to the anode as fuel and oxygen is supplied to the cathode as the oxidant. The oxygen can either be in pure form (O2) or air (a mixture of O2 and N2). PEM fuel cells typically have a membrane electrode assembly (“MEA”) in which an ion conductive solid polymer membrane has an anode catalyst on one face, and a cathode catalyst on the opposite face. Each electrode has finely divided catalyst particles (for example, platinum particles), supported on carbon particles, to promote oxidation of hydrogen at the anode and reduction of oxygen at the cathode. Electrons stripped off the hydrogen power the electric motor and then travel through the circuit to the cathode side. Protons flow from the anode through the ion conductive polymer membrane to the cathode where they combine with oxygen to form water, which is discharged from the cell. The MEA is sandwiched between a pair of porous gas diffusion layers (“GDL”), which in turn are sandwiched between a pair of non-porous, electrically conductive elements or plates. The anode and cathode gas diffusion layers of a typical PEM fuel cell are formed of porous conductive materials, such as woven graphite, graphitized sheets, or carbon paper to enable the fuel or air to disperse over the surface of the electrode. The plates function as current collectors for the anode and the cathode, and contain appropriate channels and openings formed therein for distributing the fuel cell's gaseous reactants over the surface of respective anode and cathode catalysts. In order to produce electricity efficiently, the polymer electrolyte membrane of a PEM fuel cell should be thin, chemically stable, proton transmissive, non-electrically conductive and gas impermeable. In typical applications, fuel cells are provided in arrays of many individual fuel cells called stacks in order to provide high levels of electrical power.
Although these prior art fuel cell configurations work reasonably well, significant problems arise in these devices during global or local fuel starvation and during start/stop conditions. Specifically, oxidation of electrode carbon support results in damages to the electrode structure, decreased fuel cell performance, and decreased service lifetime of the cell.
Accordingly, there is a need for fuel cell devices having electrodes that are resistant to oxidation.